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Operative Techniques in Spine Surgery

■ Correction of pelvic obliquity

■ Pelvic obliquity is common in patients with neuromuscular deformities. ■ Correction of the coronal misalignment frequently re- quires pelvic fixation. 9 ■ Other disorders ■ Less common indications include sacrectomy performed for sacral tumors, sacral fracture, and for osteoporosis in the presence of lumbosacral fusion. 20 ■ Although many techniques exist for sacropelvic fixation, only three are currently in widespread use, 11 and we will focus only on those three: the Galveston L-rod technique, 2 the iliac screw technique, 15 and the S2AI technique. 5,23 ■ A C-arm should be available for intraoperative imaging if necessary. ■ Planning the extent and type of procedure to be performed requires a thorough understanding of the anatomy of the patient’s deformity. ■ Patients with significant pelvic obliquity may have significant differences between the two sides of the pelvis, and the tra- jectory of the anchors may need to be modified accordingly. ■ Patients with significant osteoporosis may require larger size screws, up to 10 mm, in order to obtain adequate purchase. ■ Patients who have had prior bone taken from the iliac crest may not be candidates for iliac bolts and an alternative tech- nique such as the S2AI method should be used. ■ Patients with deficient iliac bone—for example, patients with sacropelvic resection for tumor—may require additional points of fixation on the intact side. ■ The patient is positioned prone on a radiolucent frame, per routine for posterior spinal procedures. ■ A transverse pad should run across the chest at the level of the shoulders. A second transverse pad should run across the pelvis at the level of the anterior superior iliac spine (ASIS). The chest wall and abdomen should be free to expand with- out touching the table to ensure adequate space for chest wall movement during ventilation. ■ The drapes should be placed distally enough to expose the start of the gluteal cleft, taking care not to drape out the PSIS. ■ The approach depends on the technique used and specific points for each technique are discussed in the following text. ■ In general, the approach for the open procedures is an exten- sion of the midline incision, centered over the spinous pro- cesses of the vertebrae, and with some modification distally based on the technique. ■ The goal should be to quickly expose the entire area of the spine that is going to be instrumented, with removal of soft tissue out to the transverse processes bilaterally. ■ The exposure should extend caudally enough to expose the dorsal S1 sacral foramen in order to allow for the placement of sacropelvic fixation. ■ The iliac screw and Galveston techniques require additional soft tissue dissection laterally out to the iliac crest in order to expose the starting point on the PSIS.

Zone 1

Zone 2

Zone 3

FIG 5 ● Zones of pelvic fixation. Biomechanical strength increases as you progress from zone 1 to zone 3. Furthermore, zone 3 allows place- ment of the instrumentation the farthest anterior to the pivot point.

Preoperative Planning

IMAGING

■ Standing full length lateral and posteroanterior (PA) plain radiographs should be obtained in all patients with a spinal deformity, to evaluate overall alignment of the spine. ■ Due to the complex and variable anatomy of the sacrum, computed tomography (CT) imaging may be helpful for planning of screw placement but is not always necessary. ■ Identification of anatomic abnormalities such as dural ecta- sia, Tarlov cyst, or prior harvesting of iliac crest bone that might alter the necessary surgical approach should be com- pleted prior to the surgical procedure. ■ The most common indication for sacropelvic fixation is a long spinal fusion to the sacrum. 11 The definition of a long spinal fusion is controversial. Most agree that fusions that cross the thoracolumbar junction and progress to the sa- crum should be augmented with pelvic anchors. However, we feel that pelvic anchors should also be considered in fusions that extend above L2 and progress to the sacrum. ■ Conditions that commonly require a long spinal fusion in- clude lumbar scoliosis in adults, children with a structural lumbosacral scoliotic curve, paralytic kyphoscoliosis, par- alytic and neuromuscular kyphoscoliosis, and congenital scoliosis. 20 ■ High-grade spondylolisthesis ■ Correction of grade III or higher spondylolisthesis places excessive force on the posterior implants. 6 ■ Instrumentation into the pelvis serves as an adjunct to the S1 pedicle screws and may reduce the incidence of pseud- arthrosis and distal implant failure. 20 ■ Flat back syndrome requiring corrective osteotomy ■ Flat back syndrome refers to the loss of lumbar lordosis following a posterior spinal fusion. 28 Patients present with pain, loss of sagittal balance, and caudal disc degeneration. ■ Correction of the deformity frequently requires osteoto- mies and a long fusion to the sacrum. 28 These fusions should be supplemented with pelvic instrumentation to decrease the risk of pseudarthrosis. SURGICAL MANAGEMENT Indications ■ Long spinal fusions

Positioning

Approach

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